In the recycling of old starch-coated printed paper such as old newspapers and magazines for use in papermaking, it is usually desirable to remove the printing ink in order to produce new paper of high brightness. It is therefore conventional to repulp (or disintegrate) the old paper together with deinking chemicals, such as deinking surfactant, NaOH and sodium silicate, followed by bleaching with hydrogen peroxide and deinking chemicals and by separation of ink particles from the pulp.
A number of documents in the prior art describe the use of enzymes to improve ink removal. Thus, Japanese laid-open patent application Kokai Sho 59-9299 (Kao), Japanese laid-open patent application Kokai Sho 63-59494 (Honshu Paper), Japanese laid-open patent application Kokai Hei 2-80683 (Oji Paper) and WO 91/14819 (Novo Nordisk) describe the use of a cellulase, i.e. an enzyme acting on the cellulose fibers of paper. Japanese laid-open patent application Kokai Hei 2-160984 (Novo Nordisk) and Japanese laid-open patent application Kokai Hei 2-80684 (Lion) describe the use of a lipase, i.e. an enzyme acting on triglycerides in the printing ink.
It is the object of this invention to provide an improved process for removal of printing ink for use in the recycling of old starch-coated paper.